Method for correcting systematic errors in a laser processing system

Abstract

A method for calibrating a laser micro-machining system in three dimensions includes scanning a sample workpiece to determine the 3D surface, calculating the best fit surfaces to the scanned data in a series of steps, and storing the results so that subsequent workpieces can be calibrated to remove systematic errors introduced by variations in an associated material handling subsystem. The method optionally uses plate bending theory to model particulate contamination and splines to fit the 3D surface in a piecewise fashion to minimize the effect of local variations on the entire surface fit.

1. A method for calibrating a workpiece processing system that includes a workpiece containing fiducial points with known locations, a chuck for holding the workpiece, a laser emitting a laser beam and optics for directing the laser beam to the workpiece, a material handling subsystem, and a control subsystem for commanding the material handling system, the optics, or both, to direct a particular point along the laser beam to a particular point on the workpiece to compensate for systematic errors in the relationship between the laser beam and the workpiece, comprising:
 performing 3D measurements of a workpiece at multiple positions to construct 3D map data corresponding to the workpiece; 
 correcting errors in X and Y locations by comparing the measured locations of fiducial points on the 3D map to their known locations; 
 calculating a first best fit surface to the 3D map data; 
 removing a first error by first surface subtraction that includes subtracting the first best fit surface from the 3D map data to form a first residual; 
 calculating a second best fit surface to the first residual formed by the first surface subtraction; 
 removing a second error by second surface subtraction that includes subtracting the second best fit surface from the first residual to form a second residual; 
 dividing the second residual formed by the second surface subtraction into multiple smaller, adjacent regions; 
 calculating a regional best fit surface to each of the multiple regions to form corresponding regional surfaces; 
 combining the X and Y location corrections, the first best fit surface, the second best fit surface, and the regional surfaces into a calibration map; 
 using the calibration map to estimate errors in the relationship between the laser beam and the workpiece; and 
 storing the calibration map for use in calibrating subsequent workpieces, thereby to enable correction of systematic errors introduced by the system. 
 
   
   
     2. The method of  claim 1  wherein the correcting errors in X and Y locations comprises comparing a polynomial fit of the measured data to the known locations first in a cross-axis direction relative to the X and Y locations and then in an along-axis direction relative to the X and Y locations. 
   
   
     3. The method of  claim 1  wherein the first, second, or regional best fit surfaces each are one of polynomial, trigonometric, or plate bending theoretic. 
   
   
     4. The method of  claim 1  wherein the calculation of the first, second, or regional best fit surface includes performing the fit in a piecewise manner in X, Y, or Z using splines. 
   
   
     5. The method of  claim 1  wherein a 3D measurement includes measuring the location of the workpiece in the X, Y, or Z axis or any combination of the three axes in a single measurement. 
   
   
     6. The method of  claim 1  wherein the 3D measurements are obtained by illuminating a feature on the workpiece with a laser. 
   
   
     7. The method of  claim 1  wherein the calibration map is improved by measuring subsequent workpieces. 
   
   
     8. The method of  claim 1  wherein the workpiece to be calibrated is a semiconductor wafer. 
   
   
     9. A method for calibrating a workpiece processing system that includes a workpiece containing known fiducial points, a chuck for holding the workpiece, a laser emitting a laser beam and optics for directing the laser beam to the workpiece, a material handling subsystem, and a control subsystem that commands the material handling system, the optics, or both, to direct a particular point along the laser beam to a particular point on the workpiece to compensate for systematic errors in the relationship between the laser beam and the workpiece, comprising:
 performing 3D measurements of a workpiece at multiple positions to construct a 3D map of the workpiece; 
 forming a calibration map by calculating multiple best fit surfaces to the workpiece, one of the best fit surfaces including multiple piecewise adjacent regions; 
 using the calibration map to estimate errors in the relationship between the laser beam and the workpiece; 
 storing the calibration map for use in calibrating subsequent workpieces; and 
 applying the calibration map to correct systematic errors introduced by the system. 
 
   
   
     10. The method of  claim 9  wherein the best fit surfaces are one of polynomial, trigonometric, or plate bending theoretic. 
   
   
     11. The method of  claim 9  wherein the calculation of each best fit surface includes performing the fit in a piecewise manner in X, Y, or Z using splines. 
   
   
     12. The method of  claim 9  wherein a 3D measurement includes measuring the location of the workpiece in the X, Y, or Z axis or any combination of the three axes in a single measurement. 
   
   
     13. The method of  claim 9  wherein the 3D measurements are obtained by illuminating a feature on the workpiece with a laser. 
   
   
     14. The method of  claim 9  wherein the calibration map is improved by measuring subsequent workpieces. 
   
   
     15. The method of  claim 9  wherein the workpiece to be calibrated is a semiconductor wafer.